Safety electric receptacle



March 1, 1966 o. HOUSTON 3,233,492

SAFETY ELECTRIC RECEPTACLE Filed Jan. 16, 1964 ill!!! Jay. 4.

Wan/1M United States Patent 3,238,492 SAFETY ELECTRHC RECEPTACLE DouglasHouston, West Hill, ()ntario, Canada, assignor to Harvey Hubbeli,incorporated, Bridgeport, Qonra, a corporation of Connecticut Filed Jan.16, 1964, Ser. No. 338,132 6 Claims. (Cl. 339-46) This invention relatesto electric receptacles and, more particularly, to such receptacles ofthe safety type.

An electric receptacle, for example, the common duplex convenienceoutlet which is widely used in home, public, and commercial buildings,presents a distinct safety hazard to small children. This is becausechildren, emboldened by curiosity, may attempt to insert metal objectssuch as hairpins or nail files into the slots in the front face of thereceptacle. Should the child thereby contact the line side of theoutlet, he may receive a serious, even a fatal shock.

A number of attempts have been made to produce a receptacle havingsafety features which would prevent the insertion of current carryingobjects into the blade-receiving slots. However, all of the attemptsheretofore made have resulted in devices having certain drawbacks. Oneapproach which has been taken in several prior art devices involves theaddition of a sliding plate, either to the cover or to the receptacleitself. The sliding plate is provided with slots for receiving the maleblades of an electrical cap. These slots are normally nonaligned withthe receptacle slots and a double motion is required to insert the cap.A first lateral motion displaces the plate so that the slots becomealigned and the blades are then inserted to make electrical contact.Several disadvantages of a construction of this type will be apparent.To begin with, the user is required to perform a double movement inorder to insert the cap. This is a commercial disadvantage and may alsobe difficult to perform under conditions of low illumination. A seconddisadvantage of such a construction is that, in most prior art devicesof this type, the movable slots are interconnected so that the properlateral motion of either slot alone will align the openings. Thisreduces the safety factor as a child could accidentally or purposelyuncover both slots with a single instrument. Still another disadvantagearises from the present trend toward the use of three wire groundingcaps and receptacles. In grounding caps of this type, the third, orgrounding, blade is a semi-cylindrical plug which has a length greaterthan that of the line blades. Accordingly, the two blades could not bemated with the movable slots on the receptacle unless some type ofspecial provision, such as an elongated grounding opening, were providedfor the grounding plug.

Those prior art devices which overcome or avoid the disadvantages setforth above, are of a relatively complex nature. Such devices mayrequire several moving parts and these moving parts tend to becomplicated and, accordingly, expensive to manufacture, sell, andmaintain.

Accordingly, it is a primary object of the present invention to providean improved electric receptacle of the safety type. Other objects are toprovide such a receptacle which allows the user to insert the cap in asingle thrusting motion, as is the case with standard receptacles; toprovide such a receptacle which cannot be actuated by insertion of aforeign object into either of the slots singly; to provide such areceptacle wherein the moving portions are few in number and are simplefiat elements which are inexpensive to manufacture; and to provide sucha receptacle which may be used with either a standard two blade cap orwith a three blade grounding cap.

Patented Mar. '1, 1956 The manner in which the foregoing objects areachieved will be more apparent from the following description, theappended claims and the figures of the attached drawing, wherein:

FIG. 1 is a front view of a grounding receptacle constructed inaccordance with this invention;

FIG. 2 is a right side view of the body of FIG. 1;

FIG. 3 is a cross section taken along the line 33 of FIG. 2,illustrating the mechanical features of the invention;

FIG. 4 is a cross section taken along the line 44 of FIG. 3 and alsoillustrating a portion of an advancing p;

FIG. 5 is a view similar to that of FIG. 3, illustrating the mechanicaloperation of the invention during insertion of a three blade groundingcap;

FIG. 6 is an illustration similar to FIGS. 3 and 5 illustrating thepositions of the mechanical elements of the receptacle when thegrounding cap is fully inserted;

FIG. 7 is an illustration similar to FIGS. 3, 5, and 6 illustrating onepossible modification of the mechanism of the invention; and

FIG. 8 is an enlarged cross section taken along the line 88 of FIG. 7.

FIGS. 1 and 2 illustrate a duplex grounding receptacle constructed inaccordance with the invention. It Will be noted that on casualinspection the receptacle presents a standard appearance and that themechanical safety features of the invention are not apparent. Thereceptacle includes a body it) which may be formed in the usual fashionfrom a suitable insulating material, such as a moldable plastic. Theface of body 10 defines individual receptacles 10a, 10b, and the back ofthe receptacle is covered by a suitable closure plate 12. Terminals 14provide means for connecting the line conductors to the receptacle linecontacts, and a binding post terminal 16 is provided for connection ofthe receptacle ground con tactto a separate ground. Each of theindividual re ceptacles, 10a, 10b, defines a pair of parallel spacedslots 18, 20 for receiving the blades of the electrical cap and asemi-circular opening 22 for receiving the grounding plug. As theconstruction of the mechanical safety features of the individualreceptacles is identical, only the features of receptacle 10a will bedescribed.

Reference to FIG. 3 will disclose that the inside of the front face ofreceptacle 18a is covered by a flat guide plate 24 apertured in a mannerto be described. Guide plate 24, in turn, is covered by a back up plate26 which serves solely to retain the moving elements of the safetymechanism and is here shown cut away to more clearly illustrate theessential features of the invention. Back up plate 26 is slotted andapertured so as not to interfere with the insertion of the blades of themale cap from slots 18, 20 or opening 22.

Guide plate 24 includes a cutout portion which defines a generallyV-shaped opening 28. The right arm of V, as viewed in FIG. 3, isessentially a parallelogram. The right hand edge 30 of the opening 28 isaligned with the outer edge of slot 18. The left arm of the V-shapedopening 28 is generally U-shaped so as to define a pair of spacedparallel slots 32, 34. The vertical edge 36 which joins the slots 32, 34is aligned with the outermost edge of the slot 20.

The right arm of V-shaped opening 28 is substantially completely filledby a female slide member 38. Slide member 38 is a planar member havinggenerally the shape of a parallelogram so as to be freely slidableWithin the right arm of opening 28. Its left edge, however, is cut awayso as to form a generally rectangular recess 40. The corners formed byrecess 40 and the left edge of member 38 are beveled and the lower leftcorner of member 38 is cut away to form an edge 42 which is parallel to3 the edge of slot 34 of the left arm of the V-shaped opening 28. Inaddition, the front surface of member 38 (that adjoining the front wallof receptacle a) is tapered over the area covering slot 18. The taperfeathers out at right edge 30, as is most clearly shown in FIG. 4.

The left arm of the V-shaped opening 28 contains a U-shaped male slidemember 44. Slide member 44 includes a pair of spaced arms 441, 442 whichare slidably positioned in the corresponding slots 32, 34. The righthand edge of male member 44 is separated from the left hand edge offemale member 38 so as to leave an intervening space. Projectingoutwardly and to the right from the right hand edge of member 44 is alocking lug 46, which is directly opposed to the recess 40 on the femalemember 38. That portion of male member 44 which covers the slot istapered in a fashion similar to the corresponding portion of the femalemember. The thin edge of the taper ends at edge 36, as is most clearlyshown in FIG. 4. A coiled compression spring 48 acts outwardly againstmembers 38, 44 retaining them in a separated condition and against theedges 30, 36 of the V-shaped opening 28.

FIGS. 3 and 4 illustrate the closed position of the safety receptacle ofthe invention. It will be noted that the slots 18, 20 are closed by thecorresponding female member 38 and male member 44. Accordingly, it isimpossible to insert a foreign object into either of these openings. Ifsuch an insertion is attempted, one of the members 38, 44 may be forcedsligthly inward along the V-shaped opening 28, but, almost immediately,misalign ment of the recess and lug 46 will occur, making it impossiblefor either of these members to be advanced sufficiently to open thecorresponding slot. The opposing beveled corners of recess 40 andlocking projection 46 will interfere and prevent further advancement, asis illustrated by dashed-dotted lines in FIG. 3. However, the operationis different when a standard electric cap 50, as shown in FIG. 4, isadvanced toward the receptacle. Cap 50 in the illustrated embodiment ofthe invention is a grounding cap of standard design, having a pair ofspaced parallel contact blades 52, 54 and a semi-cylindrical groundingplug 56. After reviewing the operation of the device, it will also beapparent that a standard two blade cap could be employed with equalfacility. As cap 50 is advanced toward the receptacle, grounding plug 56will enter the opening 22 without resistance. The ends of blades 52, 54will then contact the tapered portions of the corresponding slidemembers 38, 44 and, as they are advanced simultaneously, will begin tocam them inwardly toward each other along the arms of V-shaped opening28 as is illustrated in FIG. 5. Since blades 52, 54 are of substantiallyequal thickness, they will displace the slide members 38, 44 by equalamounts. As the angles made with the horizontal by the two arms ofV-shaped opening 28 are also equal, it necessarily follows that therecess 40 and the locking lug 46 will remain aligned with one anotherduring such relative movement of the members 38, 44 so that the lug 46will be permitted to enter the recess 40 as is illustrated in FIG. 5.The spring 48 is meanwhile being compressed by the closing force exertedby the members 38, 44 caused by the advancing cap. The interengagingaction between lug 36 and recess 46 continues until the blades 52, 54are completely inserted, as shown in FIG. 6, and electrical contact ismade with the female contacts contained within body 10. Upon withdrawingthe cap 50, the blades 52, 54 will be removed and the spring 48 willexpand, forcing the silde members 38, 44 back into their originalpositions covering the slots 18, 20.

In FIG. 7 there is illustrated a modification wherein guide plate 58 issubstituted for guide plate 24. Guide plate 58 differs from guide plate24 in that both arms of the V-shaped opening 60 resemble parallelograms.The female slide member 38 is the same. However, the male slide member62 is shaped to conform to the corresponding arm of the V-shaped opening60. A slot 64 is cut through the male member 62 and its right edge 64 isaligned with the left edge of the front slot 26. That portion of thefront surface of slide member 62 adjoining the edge 64 is tapered asillustrated in FIG. 8 to present a camrning surface to the advancingcontact blade. Upon insertion of blade 54, member 62 will be cammed tothe right in the fashion previously explained. The blade 54 will thenenter the receptacle through slot 64. It will be observed that theoperation of this modification is substantially similar to the operationof the mechanism previously described.

It will be apparent to those skilled in the art that the novel safetyreceptacle herein described achieves all the objectives set forth above.Furthermore, it will be apparent that these objectives are achieved witha minimum of complexity and with inexpensive parts. All parts of themechanism of this invention, with the exception of the spring, are fiatelements which may be easily and cheaply manufactured out of anysuitable material, such as plastic. Furthermore, there are only twomajor moving parts, so that device is reliable, rugged and inexpensive,while still providing maximum safety in its intended application. Itwill also be apparent to those skilled in the art that a number ofmodifications and variations may be made in this invention withoutdeparting from its spirit and scope. Accordingly, it is to be understoodthat the foregoing description is illustrative only rather thanlimiting. This invention is limited only by the scope of the followingclaims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electric receptacle having a body including a front walldefining at least first and second spaced slots aligned with internalfemale contacts for receiving the contact blades of an electric cap, thecombination comprising: first reciprocating member means positionable toclose said first slot; second reciprocating member means positionable toclose said second slot; first camming means on said first member meansarranged to be contacted by a first contact blade of said cap todisplace said first member means away from said first slot; secondcamming means on said second member means arranged to be contacted by asecond contact blade of said cap to displace said second member meansaway from said second slot; and control means positioned to clearinglyinterengage in response to substantially equal displacement of saidmember means to uncover said slots, but to interferingly engage uponunequal displacement of said member means to prevent furtherdisplacement and keep said slots closed; said first and said secondreciprocating member means being substantially planar and arranged to beseparately slidable along an inner surface of said front wall and alongthe arms of a V-shaped guide opening disposed in said body to uncoversaid slots when positioned at substantially the apex of said V-shapedopening and to cover said slots when positioned at substantially theouter ends of said V-shaped opening.

2. The receptacle of claim 1 wherein said control means comprises arecess defined by said first member means and a lug positioned on saidsecond member means.

3. An electric safety receptacle comprising: a body including a frontwall defining at least first and second spaced slots for receiving thecontact blades of an electric cap and enclosing female contacts thereinpositioned in alignment with said slots to mate with said contactblades; a guide plate mounted adjacent the inner surface of said frontwall defining a V-shaped cutout portion, the apex of the V beingintermediate said slots and each arm of said V being over a differentone of said slots; a first slide member positioned for sliding movementwithin said cutout portion and along one arm of said V, said first slidemember being arranged to cover said first slot at its outermost positionalong said one arm and defining along its inner edge a recess havingspaced parallel edges normal to a bisector of said V; first cammingmeans on said first slide member positioned to be contacted by a firstcontact blade of said electric cap when inserted into said first slot todisplace said first slide member toward the apex of said V; a secondslide member positioned for sliding movement Within said cutout portionand along the other arm of said V, said second slide member beingarranged to cover said second slot at its outermost position along saidother arm and carrying on its inner edge a lug protruding therefromhaving parallel edges aligned with said recess; second camming means onsaid second slide member positioned to be contacted by a second contactblade of said electric cap when inserted into said second slot todisplace said second slide member toward the apex of said V and causesaid lug to enter into said recess only upon substantially equaldisplacement of said first and second slide members toward each other;and resilient means intermediate said first and second slide membersurging said slide members outwardly from said apex.

4. The receptacle of claim 3 wherein each of said slide members issubstantially planar and wherein each of said camm-ing means comprises atapered surface portion of its corresponding slide member.

5. The receptacle of claim 4 wherein said resilient means is a spring.

6. The receptacleof claim 4 wherein said second slide member defines acontact blade receiving opening adjacent the thinnest edge of itstapered surface portion.

References Cited by the Examiner UNITED STATES PATENTS 2,545,536 3/1951Von Holtz 339-40 FOREIGN PATENTS 224,186 11/1962 Austria. 443,794 3/1936 Great Britain. 508,415 6/ 1939 Great Britain.

JOSEPH D. SEERS, Primary Examiner.

1. IN AN ELECTRIC RECEPTACLE HAVING A BODY INCLUDING A FRONT WALLDEFINING AT LEAST FIRST AND SECOND SPACED SLOTS ALIGNED WITH INTERNALFEMALE CONTACTS FOR RECEIVING THE CONTACT BLADES OF AN ELECTRIC CAP, THECOMBINATION COMPRISING: FIRST RECIPROCATING MEMBER MEANS POSITIONABLE TOCLOSE SAID FIRST SLOT; SECOND RECIPROCATING MEMBER MEANS POSITIONABLE TOCLOSE SAID SECOND SLOT; FIRST CAMMING MEANS ON SAID FIRST MEMBER MEANSARRANGED TO BE CONTACTED BY A FIRST CONTACT BLADE OF SAID CAP TODISPLACE SAID FIRST MEMBER MEANS AWAY FROM TSAID FIRST SLOT; SECONDCAMMING MEANS ON SAID SECOND MEMBER MEANS ARRANGED TO BE CONTACTED BY ASECOND CONTACT BLADE OF SAID CAP TO DISPLACE SAID SECOND MEMBER MEANSAWAY FROM SAID SECOND SLOT; AND CONTROL MEANS POSITIONED TO CLEARINGLYINTERENGAGE IN RESPONSE TO SUBSTANTIALLY EQUAL DISPLACEMENT OF SAIDMEMBER MEANS TO UNCOVER SAID SLOTS, BUT TO INTERFERINGLY ENGAGE UPONUNEQUAL DISPLACEMENT OF SAID MEMBER MEANS TO PREVENT FURTHERDISPLACEMENT AND KEEP SAID SLOTS CLOSED; SAID FIRST AND SAID SECONDRECIPROCATING MEMBER MEANS BEING SUBSTANTIALLY PLANAR AND ARRANGED TO BESEPARATELY SLIDABLE ALONG AN INNER SURFACE OF SAID FRONT WALL AND ALONGTHE ARMS OF A V-SHAPED GUIDE OPENING DISPOSED IN SAID BODY TO UNCOVERSAID SLOTS WHEN POSITIONED AT SUBSTANTIALLY THE APEX OF SAID V-SHAPEDOPENING AND TO COVER SAID SLOTS WHEN POSITIONED AT SUBSTANTIALLY THEOUTER ENDS OF SAID V-SHAPED OPENING.